Formulation and Characterization of Paraffin-based Solid Fuels Containing Novel Additives for Use in Hybrid Rocket Motors

Open Access
Larson, Daniel Bruce
Graduate Program:
Mechanical Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 26, 2012
Committee Members:
  • Kenneth K Kuo, Thesis Advisor
  • hybrid
  • rocket
  • paraffin
  • regression rate
  • LiAlH4
  • lithium aluminum hydride
  • RDX
  • MWNT
  • multi-walled carbon nanotubes
In an attempt to improve the mass burning rates of solid fuels for hybrid rocket motors, this investigation examines the impact of including various additives to paraffin wax. Several paraffin-based formulations, with additives including lithium aluminum hydride (LiAlH4), diisobutylaluminum hydride (DAH), triethylaluminum (TEA), multi-walled carbon nanotubes (MWNT), and RDX, were cast and tested. Most solid-fuel formulations were cast into paper phenolic motor casings to be tested in the Long-Grain Center-Perforated (LGCP) hybrid rocket motor located at the Pennsylvania State University’s High Pressure Combustion Lab. Casting of fuel grains containing TEA, DAH, and LiAlH4 was performed at the Aerospace Corporation. After testing a first batch of solid-fuel grains containing LiAlH4 in the LGCP hybrid rocket motor, it was determined that the particles of LiAlH4, coupled with a wax that had too low a melting point, were causing unstable, non-uniform burning. New fuel grains with ball-milled LiAlH4 ¬particles and a higher melting point wax demonstrated much more uniform burning. It was found that with 10% LiAlH4 in paraffin, the solid-fuel grains showed improved linear regression rates (7-10%) over baseline paraffin. The grains also demonstrated increased mass burn rates. Fuel samples containing MWNT were sent to the University of Texas – Austin’s Center for Nano and Molecular Science and Technology for DSC, SEM, and TGA testing. SEM results showed good dispersion of MWNT in the paraffin; however, there was local clumping of MWNT. Testing of a paraffin/MWNT fuel grain in the LGCP hybrid rocket motor showed that the paraffin/MWNT fuel grain had slightly lower regression that baseline paraffin. However, fuel grains containing MWNT have the potential for improved mechanical properties over pure paraffin. Finally, several methods of dispersing RDX in paraffin wax were attempted, but in each case, the RDX particles came out too large. The particles sank in the melted paraffin, creating a heterogeneous mixture not suitable for casting into a casting to be used in a hybrid rocket motor.